U.S. Pat. No. 6,571,756 discloses a two-stroke engine wherein an air/fuel mixture is drawn by suction into the crankcase and is moved into the combustion chamber via transfer channels during a downward travel of the piston. For reducing the scavenging losses, transfer channels, which are arranged near the outlet, are supplied with pure air via bypass channels and a controlled opening. When opening the transfer channels, pure air prestored in the bypass channel first flows into the combustion chamber whereby the afterflowing air/fuel mixture is intended to be curtained off with respect to the outlet. An essential component of the unavoidable scavenging losses, which are caused by construction, is formed by the inflowing air so that the component of the air/fuel mixture in the scavenging losses is reduced.
In practice, it has been determined that the fuel consumption and also the exhaust-gas behavior are not satisfactory, especially in two-stroke high-performance engines having a piston displacement of more than 50 cm3 to, for example, 200 cm3 and a capacity of more than 45 kW/l Vh (kilowatt per liter of piston displacement).